1. Field of the Invention
The present invention relates to novel pseudoceramides. More specifically, it relates to synthetic pseudoceramides which can be applied to soaps, shampoos, cosmetic products, food and various emulsified systems, a process for preparing the same, and dermatologic external preparations containing the same.
2. Description of the Prior Art
According to recent investigations, the glycolipid of mammal cell is reported as playing an important role in functions as a reception, response and receptor of recognition and information, differentiation, proliferation, malignant change, or behavior of cells. The glycolipid belongs to the category of so-called sphingoglycolipid and comprises i) a basic lipid structure of ceramide in which fatty acid is bonded to sphingosine by a amide bond and ii) the combination of sugars selected from the group consisting of glucose, galactose, N-acetylglucosamine, fucose and cyalic acid which are bonded to the ceramide through glycoside bonds.
Ceramide is closely related to skin aging and resilience of skin, and it is well established that ceramide has a vital role in the production and maintenance of water permeability barrier of the skin. It is understood that the resilience and appearance of skin essentially relate to water content of several layers of skin. Collagen fiber of the inner skin, an essentail part to determine skin resilience, is bonded to water molecules, which proteoglycan also is bonded to lots of water molecules. As the water content of skin is determinded by diffusion of water from inner skin side, not by support of water from outside, the damage of lipid layer totally affects on the skin condition.
Ceramides are the most prominent lipids found in stratum corneum, the outermost layer of epidermis, and have an important function in formation and retention of stratum corneum. Skin damage caused by detergents which remove the lipids essential for the barrier function will result in an increased transdermal water loss(TEWL), and deteriorated barrier function has negative consequences for the total condition of the skin. Moreover, a damaged skin barrier leads to increased skin sensitivity and potential irritation such as atopic dermatitis or psoriasis. It has been found that topical applications of ceramide- or pseudoceramide-containing compositions are effective in relieving atopic eczema. They also have been found to exhibit therapeutic properties such as wound and ulcer healing through the promotion of cell restoration and growth.
With these reasons, many extentive efforts have been made by lots of the cosmetic and pharmaceutical companies to obtain access natural ceramide or pseudoceramide effectively. The proceses for preparing ceramides are widely divided into two categories: the one for processes by means of chemical synthesis, and the other for those by means of extraction from plants(WO 92/21321), animals[H. Lambers, et al., 2nd ASCS(1995), pp.106.about.125] or yeast(WO 94/10131). The present invention relates to processes by means of synthesis.
Synthetic processes are divided into two groups: the one for synthesizing ceramides which has the same structure as natural ceramides, and the other for synthesizing pseudoceramides which have similar structure to natural ceramides. In order to synthesize a pseudoceramide, it is preferable that the structure of natural ceramides should be examined first, and then ceramides having similar structure to natural ceramides should be synthesized. Natural ceramides existing in the nature are widely divided into 6 types, and the basic structure of these natural ceramides has at least two alkyl group, at least two hydroxy group and at least one amide bond.
EP 0282816(Kao, 1988) discloses a process for preparing pseudo ceramides wherein an easily substitutable glycidyl ether is synthesized and then reacted with alkanolamine; and then fatty acid is bonded thereto by an amide bond. When a pseudoceramide is prepared according to the process, it is disadvantageous in that the glycidyl ether having epoxide group must be synthesized as it is not a commonly used compound. Further, the process required at least three step reactions to obtain final pseudoceramides.
In U.S. Pat. No. 5,221,757(Kao, 1993), disclosed are processes for preparing various pseudoceramides through 2.about.6 step reactions by using glycidyl ether, ethanolamine and fatty acid ester substituted with hydroxy group as starting materials.
The pseudoceramides according to the above-mentioned patents have ether bonds which are not be found in natural ceramides, and some of them do not have amide bond. In addition, these patents are disadvantageous in that the process for preparation is relatively complicated and requires high production cost.
WO 92/06982(Unilever, 1992) discloses the preparation of pseudoceramides having two different general forms, and their application to cosmetic compositions. The pseudoceramides described in the patent are characterized in that the hydroxy group has been transformed by phosphorylation or sulfation of the compounds having similar basic skeleton to those of EP 0282816. However, this process also is disadvantageous in that the process for preparation requires many steps and much cost.
WO 92/03129(Duke Univ., 1992) discloses an invention relating to pseudoceramides having a basic structure of natural ceramides. However, the patent was limited in its-industrial use.